The present invention relates to a touch panel switch used as an input operation unit for electronic equipment to feed an input signal by pushing the touch panel switch with a finger, a pen and the like.
In recent years, many flat touch panel switches have been used as an input operation unit for electronic equipment to perform an inputting operation by applying a small finger pressure, a pen and the like.
Particularly, as portable small information equipment having a variety of functions is prevailing rapidly, the demand for transparent touch panel switches overlaid on a liquid crystal display (referred to as LCD, hereafter) to perform an input operation according to instructions displayed on the LCD, is growing.
A description is given to a prior art touch panel switch as such with reference to the drawings.
In order to facilitate the understanding of structural details of the touch panel switch, the drawings are prepared with the dimensions in thickness directions stretched.
FIG. 6 is a cross-sectional view of a prior art transparent touch panel switch. In FIG. 6, transparent thin film-like first electrode 20 formed of indium oxide (referred to as ITO, hereafter) containing tin is provided on the bottom surface of transparent and flexible insulating sheet 10.
On the upper surface of transparent insulating substrate 30 formed of glass and the like and located underneath aforementioned insulating sheet 10 is disposed second electrode 40, which is formed of ITO and the like, facing aforementioned first electrode 20 with a predetermined spacing provided therebetween.
In order to have first electrode 20 formed on insulating sheet 10 and second electrode 40 formed on insulating substrate 30 facing each other and separated by a predetermined distance from each other, adhesive 50 is applied to the peripheral edges of insulating sheet 10 and insulating layer 60 is applied on the peripheral edges of insulating substrate 30 at the side of second electrode 40. And then both adhesive 50 and insulating layer 60 are fixed together to have a predetermined combined thickness. Thereby, a switch contact is formed between first electrode 20 located towards inside from the place where adhesive 50 and insulating layer 60 are fixed together, and second electrode 40, thus producing a transparent touch panel switch.
Next, a description is made on how a touch panel switch thus structured operates.
A transparent touch panel switch as described above is usually disposed on display devices such as LCD installed on electronic equipment, thereby forming an overlaid structure.
In other words, since the user of electronic equipment is allowed to read operational instructions and pieces of selected information legibly through the touch panel switch, a pushing action applied to the upper surface of insulating sheet 10 of the touch panel switch is carried out with a finger, a pen and the like in accordance with the operational instructions and pieces of selected information, thereby allowing the input operation to have the electronic equipment operated as required.
A description is given to how the touch panel switch operates at that time. Upon being pushed by a finger or a pen, flexible insulating sheet 10 bends downward and first electrode 20 on the bottom surface of insulating sheet 10 is brought into contact with second electrode 40 on insulating substrate 30 to turn on the touch panel switch, thereby allowing a signal to be fed to a circuit of the electronic equipment connected to first electrode 20 and second electrode 40.
Electronic equipment adopting such a touch panel switch as above is generally provided with a display screen that is large enough to cope with the applications thereof and also with a touch panel switch comparable to the display screen in size, through which an input operation is allowed to be performed. A control circuit of the electronic equipment has a plurality of operational instructions and pieces of selected information displayed on the display screen simultaneously, and signals corresponding to positions, where respective operational instructions and pieces of selected information are displayed, are outputted from a touch panel switch, thereby allowing the electronic equipment to behave as the operator thereof desires.
However, in the prior art touch panel switch as described above, when an input operation is performed by pushing insulating sheet 10, the pushing down step involves a downward displacement distance equaling the combined thickness of adhesive 50 and insulating layer 60, thereby applying a great deal of stress to insulating sheet 10 and first electrode 20 formed of ITO and disposed on the bottom surface thereof. Particularly, the stress is remarkable when the peripheral area of the touch panel switch, i.e., the vicinity of the area, where adhesive 50 and insulating layer 60 are fixed together, is pushed as a partially enlarged cross-sectional view of FIG. 7 shows.
When an input operation is repeated in the vicinity of the areas, where adhesive 50 and insulating layer 60 are fixed together, the function of thin film like first electrode 20 as an electrode tends to be deteriorated at the pushed position and in the vicinity thereof due to the stress, thereby hindering sometimes the generation of a predetermined input signal.
With the aforementioned prior art touch panel switch, in order to have plane electrodes facing each other with a predetermined spacing formed therebetween, an insulating sheet and an insulating substrate, each provided with the electrodes, are fixed by adhesion onto a predetermined position, respectively, with an insulating layer placed therebetween, thereby allowing the areas except for the area, where the insulating sheet and insulating substrate are fixed together, to function as a switch. When the pushing action is repeated in the vicinity of the area of fixing together, the peripheral areas of a touch panel switch near the area of fixing together are not allowed to be used as input operation areas to act as switch contacts from the point of reliability due to the functional vulnerability of the plane electrodes. As a result, a problem of shrinkage in the effectively usable area for an input operation is presented.
Although a description is made in the Japanese Patent Laid-Open Application No.H04-143823 to the effect that an adoption of an elastic body disposed on the input operation area as a gap maintaining material improves the reliability against a repetitive application of a pressing force to one and the same place, a double-faced adhesive framework material is used on the peripheral areas and no disclosure is made on countermeasures to prevent the vicinity of the peripheral areas from becoming deteriorated. Also, a description on an example of using an elastic body as a spacer for the peripheral areas is carried in the Japanese Patent Laid-Open Application No. H04-123728. However, the spacer is intended for solving the problem of sagging of a film due to heat and moisture by fixing an elastic body applied with an adhesive on both surfaces thereof in place. Therefore, the spacer can be anything as far as it is formed of an elastic body and what are described in the exemplary embodiment are such foam materials as urethane and rubber. Any solutions of the aforementioned problem of an input operation area shrinking in the peripheral areas are not disclosed.
The present invention deals with the foregoing problem and aims at providing a touch panel switch, in which an effectively usable area is allowed to be expanded.
In order to achieve the aforementioned objective, a touch panel switch of the present invention comprises:
a flexible insulating sheet having a first electrode; and
an insulating substrate having a second electrode,
in which both electrodes are facing each other with a spacer provided therebetween on peripheral areas of the touch panel switch, and
the spacer is an elastic body with a coefficient of elasticity ranging from 1xc3x97105 dyne/cm2to 1xc3x97107 dyne/cm2.
Since an insulating layer has an appropriate magnitude of elasticity, even when a pressing force is applied to the flexible insulating sheet in the vicinity of the area where the flexible insulating sheet and insulating substrate are fixed together, the insulating layer is deformed in the direction to reduce the thickness thereof in accordance with the bending of the flexible insulating sheet, thereby reducing a deforming stress imposed to the flexible insulating sheet and the first electrode disposed on the bottom surface thereof. As a result, the functional deterioration of the first electrode is suppressed and the area usable as a switch contact is expanded.